Trapping devices are described in U.K. Pat. No. 1,062,701 and U.S. Pat. No. 4,010,101. These devices have walls defining a settling chamber. A foraminous element is provided in each device and arranged in such a way that liquid flowing from an inlet opening to an outlet opening will pass at least once through the foraminous element, separation of foreign liquid resulting from the passage of the supply liquid through the device in such a way that separated foreign liquids settle in the settling chamber.
A manually operated drain outlet valve was originally provided for the lower region of the settling chamber to permit foreign liquids which are separated out and trapped in the settling chamber, to be drained from the chamber after a warning signal had been provided in response to a float-operated detecting system.
U.S. Pat. No. 4,264,442 also disclosed a trapping device with means for separating such foreign liquids from the supply liquid as the foreign liquids and supply liquid pass through a settling chamber having a lower zone for receiving foreign liquids having a specific gravity higher than that of a supply liquid. Detector contacts extended into the chamber for detecting the presence in the settling chamber of such foreign liquids, and an educer-operated drain outlet valve was provided for draining the settling chamber. This valve required an educer having a flow passage connectable to a compressed air source, whereby flow of compressed air through said air passage created suitable low pressure conditions in a valve chamber for moving a valve member clear of a valve seat and permitting foreign liquids to flow through a drain opening and from said settling chamber. However, this requires compressed air lines from a compressed air source.
In addition, the detector contacts, which were intended to replace the float-operated detecting systems of the earlier patent specifications, could be actuated more readily by splashing of the foreign liquids, and was not wholly successful. It is therefore desirable to provide an improved drain system which preferably operates without the need for a compressed air supply.